1. Field of the Invention
This invention relates generally to tools for setting fasteners having pin members with pull grooves and more particularly concerns a compact nose assembly for lockbolt installation tools. The nose assembly is designed to minimize deflection between a collet and anvil during swaging of a collar about a pin member.
2. Description of Prior Developments
A demand has arisen for a rigid yet compact installation tool for setting fasteners of the lockbolt type. A tool is required which can access and install such fasteners which are located between closely spaced panels or within a small clearance space. To satisfy this demand, various attempts have been made to provide an offset nose assembly including an anvil and collect for swaging a fastener collar about a grooved fastener pin. In such designs, the swaging anvil is radially offset from the axis of the piston which drives the anvil against the collar. This arrangement allows the radially offset anvil portion of the nose assembly to access and set fasteners without interference from the anvil housing and/or from the body of the installation tool.
By offsetting the axis of the fastener pin and collar assembly from the axis of the tool piston, large bending forces are generated within the nose assembly during swaging of the collar around the pin. These bending forces have heretofore resulted in deflection between the anvil and collet as well as deflection of the entire nose assembly with respect to the body of the installation tool and with respect to the pin and collar. This deflection has typically resulted in the application of a radial force to the pin and has caused radial deflection of the pin during setting of the fastener. This radial deflection, when tranmitted and applied to the fastener pin, has caused premature and/or uncontrolled pin breakage resulting in defective connections between the pin and collar. This problem is particularly acute when titanium alloyed pins are used since these pins are most sensitive to radial loading and will easily shear under such radial loads before the collar is fully set.
To prevent this undesirable result, prior designs have attempted to resist the deflection of offset nose assemblies by increasing the size and mass of the anvil housing, the collet and the threaded collet stud which connects the collet to the tool. These massive and bulky assemblies thus attempted to provide the necessary rigidity within the nose assembly per se. While such designs have generally performed satisfactorily, they have not been able to access extremely close or cramped installation sites due to their relatively large and massive construction. That is, in order to stiffen the nose assembly, prior anvil housings and collets have been designed with thick cross sections thereby resulting in relatively bulky and wide contours incapable of reaching within small spaces.
Accordingly, a need exists for a compact offset nose assembly which resists deflection under load, prevents undesirable pin deflection, avoids premature and/or uncontrolled pin failure yet is more compact than prior designs so as to allow access of the nose assembly within tight or cramped spaces.